This invention relates generally to a method and apparatus for interfacing to nerves and, more particularly, to a method and apparatus for obtaining electrical signals from the nervous system.
Prosthetic devices have been developed that use self-generated electrical signals as control signals. For example, the "Boston Arm," an above-elbow prosthesis that performs flexion and extension of the elbow, uses the myoelectric signals (EMG) from the biceps and triceps muscles to control a movement that these prime-mover muscles naturally performed in the preamputated limb. Although such control is useful to the amputee, it would be desirable to increase the mobility of the Boston Arm by incorporating additional controlled movements (such as pronation, supination, opening and closing of the hand) in the artificial limb. Unfortunately, the muscles normally controlling these functions are in the forearm and hand and, therefore, they are no longer present in above-elbow amputees. However, the nerves (median, radial, ulnar and musculocutaneous) that contained the motor neurons to these muscles are accessible in the remaining part of the arm. Thus, improved control of the Boston Arm could be achieved by obtaining chronic direct accessibility to the electrical signals in the peripheral nervous system. The ultimate objective would be to chronically obtain distinguishable nerve signals associated with functionally distinct movements of a limb. It would then be possible to use the nerve signals to activate and control an upper-limb prosthesis with multiple degrees of freedom.
Previous attempts to record voluntarily elicited nerve signals for the expressed purpose of controlling a prosthesis have encountered technical and physiological restrictions that prevented the recording of reliable signals. Attainment of such signals requires electrical interface to the nerve with an electrical device capable of; a good mechanical connection with the nerve trunk to minimize the relative movement of the electrode and nerve; providing a good signal-to-noise ratio; disregarding the concurring EMG signals from adjacent muscles; and causing minimum physical damage and few physiological restrictions to the nerve. Furthermore, all the materials used to construct the device must be biocompatible and have sufficient structural ruggedness to remain operational for lengthy periods of use.
The object of the invention, therefore, is to provide an electrical device for obtaining chronic direct accessibility to the electrical signals in the peripheral nervous system.